1. Field of the Invention
This invention relates generally to a dental instrument and, more particularly, to trays for obtaining an impression of a patient's dentition.
2. Description of the Relevant Technology
Dental impression trays for obtaining an impression of a patient's dentition are known. Such trays generally include tray portions anatomically contoured to fit at least a part of a patient's upper and/or lower oral anatomy, of which an impression is to be obtained. There are mainly two techniques to taking dental impressions; the single arch and the closed bite technique. In the closed bite technique, the tray portion is loaded with a suitable dental impression material and situated over the part of the patient's oral anatomy of which an impression is desired. The patient then bites into the impression material to form an impression of the patient's oral anatomy in the impression material. After the impression material sets, it is used as a mold, into which plaster or dental stone can be poured which upon setting forms a model of the patient's oral anatomy. In addition, the set impression material may also be used directly as a mold for other purposes such as the fabrication of temporary restorations, the process of teeth whitening etc. A problem encountered in the use of conventional dental impression trays is that as and after the impression is taken and before and after the material sets, the impression material tends to move with respect to the wall or walls defining the tray portion. In particular, as the impression material starts to set while the impression is being taken, the soft impression material tends to separate from the wall and move inwardly into the tray portion and also tends to spread laterally along the wall. Moreover, after the impression is taken, the impression material tends to be lifted out and away from the dental impression tray walls as the patient's oral anatomy is removed from the impression material. Such a movement of the impression material distorts the impression obtained resulting in an ill-fitting dental product i.e. crown, bleaching tray, partial denture, restoration, etc.
Attempts have been made to prevent the soft impression material from moving in the manner described above. For example, sticky impression adhesives are available which are applied to the tray wall prior to the tray portion being loaded with impression material. However, the use of dental tray adhesives is not entirely satisfactory, as the distortion of the dental impression is not completely eliminated. Furthermore, the use of adhesives requires an additional step in the impression procedure and the application of adhesives to the dental tray is quite messy. In an impression tray available from Premier Dental Products, a corporation of Plymouth Meeting, Pa. and illustrated in U.S. Patent No. Des. 266,269 and 277,605, a series of vertically extended ribs are formed in the tray wall, which at least to some extent inhibit lateral spreading of the impression material along the tray wall. However, the impression material still tends to separate from the wall and move inwardly into the tray as well as to be lifted out of the tray when the teeth are removed from the impression material.
U.S. Pat. No. 4,689,010 to Wolfe describes a dental impression tray which includes a tray portion anatomically contoured to fit over at least a part of the patient's upper and/or lower dentition of which an impression is to be obtained. The tray portion is defined by at least one wall, on which a plurality of vertically extending adjacent ribs are integrally formed defining a plurality of channels there between, into which the impression material flows. Each rib has a dovetail cross section so that the channels narrow or converge in the inward direction, i.e. towards the interior of the tray portion, to prevent the impression material from separating from the side wall in the inward direction as well as spreading laterally after the impression is taken. In this design each rib may be further provided with a lower surface situated within the tray portion and under which the impression material flows when the tray is loaded with impression material to prevent the impression material from being lifted out of the tray when the teeth are removed from the impression material. However the lower surface situated underneath each rib of Wolfe's dental impression tray makes it difficult to produce by common manufacturing techniques such as injection molding. In fact, U.S. Pat. No. 5,316,474 to Robertson tries to address some of the deficiencies in Wolfe's dental impression tray by providing a tray made with a low memory material.
Lastly, Wolfe's design cannot be used with a soft impression material such as alginate because the tray walls are too small to provide enough retention force to prevent the alginate impression material from distorting when the impression tray is being removed from the patient's mouth.
U.S. Pat. No. 5,733,118 to Pankuch et al. discloses a dental impression tray contoured to fit over at least a portion of a patient's dentition. The dental impression tray includes a first wall portion, a second wall portion substantially parallel with the first wall portion and an elongate rib to connect these two wall portions to form a channel between those two walls. Upon taking an impression of a patient's teeth, the impression material flows into the channel so that the impression material is more securely held in the tray upon its removal from the patient's teeth. However, this design suffers the similar drawback as the Wolfe's tray because it does not provide a 360° lock (locking the top, bottom, and both side edges of the wall) of the impression material by the tray walls. Instead it only provides an 180° lock (locking the top and bottom edges of the walls). In addition, for the material to be locked by the channels, the impression material has to overflow into the channel from the top of the walls. Therefore, the efficiency of forming a lock between the walls is dramatically decreased, especially for those quick setting materials. It has also been shown that this type of design is not suitable for the soft alginate dental impression materials because it does not provide enough retention force for these materials.
Currently, two of the most popular dental impression materials used by dental professionals are the vinyl polysiloxane (VPS) and the alginate-based impression materials. In fact dental professionals take millions of these types of impressions each year. Alginate is one of the most popular impression materials due to its accuracy, ease of removal from the teeth, inexpensive price, and ease of use. The VPS's are quite popular because they are extremely accurate, rigid, dimensionally stable, and give predictable results; although they are much more expensive. Therefore, a need exists to help dental health professionals to take these impressions using the most popular impression materials more conveniently.
Accordingly, it is an objective of certain embodiments of the present invention to provide a dental impression tray that provides enough retentive force for soft impression materials, such as alginate impression materials, upon taking a dental impression.
It is a second objective of certain embodiments of the present invention to provide a dental impression tray that provides more retentive force for the rigid, dimensionally stable impression materials, such as the vinylpolysiloxane impression materials.
It is a third objective of certain embodiments of the present invention to eliminate the need for adhesives for most impression materials by incorporating additional mechanical retention into a dental impression tray itself.
It is a fourth objective of certain embodiments of the present invention to provide a closed bite dental impression tray that can be easily removed from a patient's mouth after the impression has been taken by providing one or more purchase points on the lateral aspect of the dental tray.